Benefit Plans and Other Postretirement Benefits (Details) $ in Millions		1 Months Ended	3 Months Ended		6 Months Ended
		Jan. 31, 2019 USD ($) Plan	Jun. 30, 2019 USD ($)	Jun. 30, 2018 USD ($)	Jun. 30, 2019 USD ($)	Jun. 30, 2018 USD ($)
Pension Plan [Member]
Components of Net Periodic Benefit Cost [Abstract]
Service cost			$ 1.1	$ 1.2	$ 2.2	$ 2.4
Interest cost	[1]		1.4	1.4	2.9	2.7
Expected return on plan assets	[1]		(2.0)	(2.3)	(4.2)	(4.5)
Amortization of prior service cost (credit)	[1]		0.0	0.0	0.0	0.0
Defined Benefit Plan, Amortization of Gain (Loss)	[1]		1.1	1.4	2.2	2.8
Defined Benefit Plan Net Benefit Cost (Credit) Recognized Before Regulatory Adjustments			1.6	1.7	3.1	3.4
Defined Benefit Plan Credits Not Recognized Due To Effects of Regulation			0.0	0.0	0.2	0.2
Defined Benefit Plan, Net Periodic Benefit Cost (Credit)			1.6	1.7	3.3	3.6
Total contributions to the pension plans during the period		$ 7.0
Other Postretirement Benefits Plan [Member]
Components of Net Periodic Benefit Cost [Abstract]
Service cost			0.0	0.0	0.0	0.0
Interest cost	[1]		0.1	0.2	0.3	0.3
Expected return on plan assets	[1]		0.0	0.0	0.0	0.0
Amortization of prior service cost (credit)	[1]		(0.1)	(0.1)	(0.2)	(0.2)
Defined Benefit Plan, Amortization of Gain (Loss)	[1]		0.1	0.1	0.1	0.3
Defined Benefit Plan Net Benefit Cost (Credit) Recognized Before Regulatory Adjustments			0.1	0.2	0.2	0.4
Defined Benefit Plan Credits Not Recognized Due To Effects of Regulation			0.0	0.0	0.0	0.0
Defined Benefit Plan, Net Periodic Benefit Cost (Credit)			$ 0.1	$ 0.2	$ 0.2	$ 0.4
Xcel Energy Inc. | Pension Plan [Member]
Components of Net Periodic Benefit Cost [Abstract]
Total contributions to the pension plans during the period		$ 150.0
Number of Xcel Energy's pension plans to which contributions were made | Plan		4

[1] The components of net periodic cost other than the service cost component are included in the line item “other expense, net” in the consolidated statement of income or capitalized on the consolidated balance sheet as a regulatory asset.